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L. Deng, R. Manny, C. Crossnoe, J. Gwiazda; Longitudinal Measures of Intraocular Pressure and Axial Length in a Subgroup of Children in the Correction of Myopia Evaluation Trial (COMET). Invest. Ophthalmol. Vis. Sci. 2007;48(13):4829.
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To investigate the association between intraocular pressure (IOP) and axial length (AL) over five years in a subgroup of children enrolled in COMET.
IOP (Tonopen), AL by A-scan ultrasonography (Sonomed) and refractive error by cycloplegic autorefraction (Nidak) in the right eye were measured at baseline and over the next 5 years in 104/118 myopic children in COMET at the Houston site. ANOVA was used to compare AL change over 5 years across 4 ethnicity groups. Regression analyses studied the association between IOP and AL change over the 5-year follow-up.
At baseline mean AL was 24.1mm+/-0.643 and mean refractive error was -2.34D +/- 0.88. Mean AL increased 0.99mm+/-0.50 over five years. African-Americans had significantly less increase in AL (n=17, 0.78 mm+/-0.43) than Whites (n=25, 1.10mm+/-0.52, p-value<0.05) but not Asians (n=7, 0.94mm +/-0.52) or Hispanics (n=50, 1.00mm +/-0.51). Baseline IOP was 15.918mmHg and it decreased 0.149mmHg over 5 years. IOP, averaged over the 6 visits, was 15.787 mmHg +/-2.82. The average IOP of African-Americans (17.88 mmHg) was higher than that of Hispanics (15.77 mmHg, p = 0.006) and Whites (14.51 mmHg, p = 0.001), but not Asians (16.26 mmHg). There was no significant association between IOP at baseline and AL change, and no significant association between IOP change and AL change over five years when examined either as continuous or categorical variables. There was a strong correlation between axial elongation and myopia progression over five years (r=-0.89). Because of this high correlation there was also no significant association between IOP and refractive error change.
Small but significant ethnic differences were noted in the IOP of myopic children. Small but significant ethnic differences were also found in axial elongation. With the highest IOP, African-Americans had the least AL change over 5 years. The absence of an association between IOP and myopia progression does not support theories linking these two factors.
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